中文摘要：

采用双区加热和液态金属冷却法（LMC）相结合,对一种含4%Re（质量分数）的镍基单晶高温合金进行了高温度梯度定向凝固。结果表明：与传统的＂高速凝固法（HRS）＂（温度梯度G=20—40 K/cm,抽拉速率V=50—100μm/s,一次枝晶间距λ_1=200—400μm）相比,该技术可以显著提高凝固界面前沿的温度梯度（G=238 K/cm）和抽拉速率（V=500μm/s）。随着抽拉速率的提高,凝固界面形态呈现出平面、胞状、粗大枝晶和细枝晶形态,一次枝晶间距不断减小,通过固态相变析出的γ′强化相也被显著细化,当G=238 K/cm,V=500μm/s时,λ_1和枝晶干γ′相平均尺寸分别减小到61.3和0.04μm。电子探针测定表明,随着抽拉速率的提高,枝晶偏析呈现先增大后减小的趋势。这是高温度梯度条件下,固相反扩散作用强烈影响元素在枝晶中分布的结果。

英文摘要：

In order to understand the effect of high thermal gradient on the microsegregation of refractory elements in Ni-based superalloys,a Ni-based single crystal superalloy containing 4% Re（mass fraction） was prepared by dual heating zone melting and liquid-metal cooling（LMC） directional solidification technique.Comparing with the traditional high rate solidification（HRS） method with thermal gradient G=20—40 K/cm,withdrawal rate V=50—100μm/s and primary dendritic arm spacingλ_1=200—400μm,this technique can significantly increase the thermal gradient（up to 238 K/cm） and withdrawal rates（up to 500μm/s）.Planar-like and cellular-like solid-liquid interfaces,coarse dendrite and fine dendrite were sequentially obtained with increasing withdrawal rates.Under the condition of G=238 K/cm and V=500μm/s,the primary dendritic arm spacingλ_1 and the mean size ofγ＇ precipitates（in dendrite core） obviously decreased to 61.3 and 0.04μm,respectively.In addition,the microsegregation increased initially and then decreased with increasing withdrawal rate,especially for the microsegregations of W and Re.EPMA line scan indicated that solid-back diffusion has an obvious influence on the microsegregation for the fine dendrite structure under high thermal gradient directional solidification.